Geologic Time Scale Fossils and Dating Geologic Time

Geologic Time Scale • Represents the history of Earth. • Earth is thought to

Major Events of each Era • Precambrian – Earth forms – First life (unicellular)

Major Events of each Era • Mesozoic – Dinosaurs, large animals – 1 st

EXTINCTION ØAbout 99% of organisms have become extinct. ØOften occurs due to natural selection,

HOW IS AGE DETERMINED? ØRelative datingØEstimates when an organism lived by comparing the location

Index Fossils • Fossil from a “known” time period. • Used to date fossils

HOW IS AGE DETERMINED? ØRadioactive dating: ØFind age by comparing the amount of decayed

Fossils • Preserved bones or other traces of ancient organisms. • Found in layers

How Fossils Form • Petrification – Occurs when rock-like minerals replace organic tissue. •

How Fossils Form • Amber: organisms become trapped in tree sap that hardens. •

Transitional Fossils • Link modern organisms to extinct organisms.

Why is the fossil record incomplete? • Not all organisms that have ever lived

Slides: 14

Download presentation

Geologic Time Scale, Fossils, and Dating

Geologic Time Scale • Represents the history of Earth. • Earth is thought to be about 4. 5 billion years old. • Timeline is broken down as follows: – Eras – Periods

Major Events of each Era • Precambrian – Earth forms – First life (unicellular) • Oxygen produced by life forms • Paleozoic – Oxygen levels increase – First insects, plants, amphibians, marine animals – Pangea forms

Major Events of each Era • Mesozoic – Dinosaurs, large animals – 1 st birds, mammals, flowering plants – Pangea breaks up • Cenozoic – Mass extinction of large mammals – Mammals dominate – Humans appear

EXTINCTION ØAbout 99% of organisms have become extinct. ØOften occurs due to natural selection, may open opportunity for new species to develop. ØMass extinctions destroy many species at a global level. Caused by catastrophic events (meteors, volcanic eruptions).

HOW IS AGE DETERMINED? ØRelative datingØEstimates when an organism lived by comparing the location of fossils in layers of rock. ØOlder organisms are in lower layers, younger organisms are in top layers.

Index Fossils • Fossil from a “known” time period. • Used to date fossils in corresponding layers.

HOW IS AGE DETERMINED? ØRadioactive dating: ØFind age by comparing the amount of decayed material to material that is not decayed. ØHalf-life = the amount of time it takes for half of the material to decay. ØCarbon-14 decays to nitrogen (5730 yrs) Ø Uranium decays to lead (700 million years)

Fossils • Preserved bones or other traces of ancient organisms. • Found in layers of sedimentary rock. • Shows how species may have changed through time.

How Fossils Form • Petrification – Occurs when rock-like minerals replace organic tissue. • Cast – Dead organism is covered with sediment, all original tissue is removed leaving a mold.

How Fossils Form • Amber: organisms become trapped in tree sap that hardens. • Ice: organisms are preserved when encased in ice. • Trace fossil: records activity of organisms. Ex: footprints, nests.

Transitional Fossils • Link modern organisms to extinct organisms.

Why is the fossil record incomplete? • Not all organisms that have ever lived became fossilized because specific conditions are needed for fossils to form.